OFDM communications methods and apparatus
OFDM signal communication methods and apparatus are described. In accordance with the invention OFDM signals are generated in the time domain with symbols being mapped to specific points in time. Training symbols may be included in the transmitted OFDM signal to facilitate symbol recovery. An exemplary receiver of the invention receives the OFDM signal from the communications channel, converts it into the frequency domain, and then filters it in the frequency domain to eliminate tones corresponding to other users. The filtered signal free of MAC interference is then converted into the time domain where channel estimation and compensation operations are performed. After channel compensation symbol recovery is performed in the time domain.
1. A method of generating a frequency division multiplexed signal at a communications device for transmission in a wireless communication system, comprising:
obtaining, by the communications device, one or more sets of M complex data symbols for transmission using a set of M tones allocated to the communications device for a dwell period comprising a plurality of symbol periods, wherein the set of M tones is a subset of tones in an available bandwidth;
generating, by the communications device, one or more sets of M signal coefficients based at least in part on the one or more sets of M complex data symbols, wherein the one or more sets of M signal coefficients are mapped to the set of M tones for one or more symbol periods of the plurality of symbol periods of the dwell period, wherein generating the one or more sets of M signal coefficients comprises generating each of the one or more sets of M signal coefficients by performing a summation of a product of a set of M complex data symbols of the one or more sets of M complex data symbols and M complex sinusoids corresponding to the set of M tones;
mapping, by the communications device, at least one set of M training symbols to the set of M tones for at least one symbol period of the plurality of symbol periods of the dwell period;
processing, for each symbol period of the plurality of symbol periods of the dwell period, a corresponding set of M mapped symbols of the one or more sets of M signal coefficients and the at least one set of M training symbols to obtain the frequency division multiplexed signal for the each symbol period of the plurality of symbol periods of the dwell period; and
transmitting, by the communications device, the frequency division multiplexed signal in the wireless communication system.
2. The method of claim 1 , wherein processing the corresponding set of M mapped symbols for the each symbol period is performed according to a function that defines a continuous-time signal corresponding to the frequency division multiplexed signal for the each symbol period, and wherein the function comprises a summation of M sinusoids having coefficients corresponding to the set of M mapped symbols for the each symbol period.
3. The method of claim 1 , further comprising:
prepending a cyclic prefix to the frequency division multiplexed signal.
4. The method of claim 1 , wherein the at least one set of M training symbols comprises a set of predetermined symbol values.
5. The method of claim 1 , wherein the at least one symbol period comprises a symbol period at or near the center of the dwell period.
6. The method of claim 1 , wherein the set of M tones comprises M contiguous tones.
7. The method of claim 1 , wherein the set of M tones comprises equally spaced tones.
8. A method of generating a frequency division multiplexed signal at a communications device for transmission in a wireless communication system, comprising:
determining, by the communications device, a first set of M tones allocated to the communications device for a first dwell period comprising a first plurality of symbol periods and a second, different set of M tones allocated to the communications device for transmission in a second dwell period comprising a second plurality of symbol periods, the first and second sets of M tones being a subset of tones in an available bandwidth;
generating, by the communications device, one or more sets of M data symbols for mapping to the first and second sets of M tones by performing a summation of a product of a set of M complex time domain data symbols and a set of M complex sinusoids corresponding to the first or second sets of M tones, respectively;
mapping, by the communications device, the one or more sets of M data symbols to the first set of M tones for one or more symbol periods of the first dwell period and to the second set of M tones for one or more symbol periods of the second dwell period;
processing, for each symbol period of the one or more symbol periods of the first and second dwell periods, a corresponding set of M mapped symbols to obtain the frequency division multiplexed signal for the each symbol period for the first and second dwell periods; and
transmitting, by the communications device, the frequency division multiplexed signal in the wireless communication system.
9. The method of claim 8 , wherein the second dwell period comprises a dwell period immediately following the first dwell period.
10. The method of claim 8 , wherein processing the corresponding set of M mapped symbols for the each symbol period is performed according to a function that defines a continuous-time signal corresponding to the frequency division multiplexed signal for the each symbol period, and wherein the function comprises a summation of M sinusoids having coefficients corresponding to the set of M mapped symbols for the each symbol period.
11. The method of claim 8 , further comprising:
prepending a cyclic prefix to the frequency division multiplexed signal.
12. The method of claim 8 , wherein the first and second sets of M tones comprise M contiguous tones.
13. The method of claim 8 , wherein the first and second sets of M tones comprise equally spaced tones.
14. An apparatus for generating a frequency division multiplexed signal at a communications device for transmission in a wireless communication system, comprising:
a time to frequency domain signal transformer for generating one or more sets of M signal coefficients for transmission using a set of M tones allocated to the communications device for a dwell period comprising a plurality of symbol periods, the one or more sets of M signal coefficients generated based at least in part on one or more sets of M complex data symbols obtained for transmission using the set of M tones in the dwell period, wherein the set of M tones is a subset of tones in an available bandwidth, wherein the one or more sets of M signal coefficients are mapped to the set of M tones for one or more symbol periods of the plurality of symbol periods of the dwell period, and wherein the time to frequency domain signal transformer generates each of the one or more sets of M signal coefficients by performing a summation of a product of a set of M complex data symbols of the one or more sets of M complex data symbols and M complex sinusoids corresponding to the M tones;
a mapper for mapping at least one set of M training symbols to the set of M tones for at least one symbol period of the plurality of symbol periods of the dwell period;
a frequency to time domain transformer for processing, for each symbol period of the plurality of symbol periods of the dwell period, a corresponding set of M mapped symbols of the one or more sets of M signal coefficients and the at least one set of M training symbols to obtain the frequency division multiplexed signal for the each symbol period of the plurality of symbol periods of the dwell period; and
a transmitter for transmitting the frequency division multiplexed signal in the wireless communication system.
15. The apparatus of claim 14 , wherein the frequency to time domain transformer processes the corresponding set of M mapped symbols according to a function that defines a continuous-time signal corresponding to the frequency division multiplexed signal for the each symbol period, and wherein the function comprises a summation of M sinusoids having coefficients corresponding to the set of M mapped symbols for the each symbol period.
16. The apparatus of claim 14 , further comprising:
a cyclic prefix inserter for prepending a cyclic prefix to the frequency division multiplexed signal.
17. The apparatus of claim 14 , wherein the at least one set of M training symbols comprises a set of predetermined symbol values.
18. The apparatus of claim 14 , wherein the at least one symbol period comprises a symbol period at or near the center of the dwell period.
19. The apparatus of claim 14 , wherein the set of M tones comprises M contiguous tones.
20. The apparatus of claim 14 , wherein the set of M tones comprises equally spaced tones.
21. An apparatus for generating a frequency division multiplexed signal at a communications device for transmission in a wireless communication system, comprising:
a time to frequency domain signal transformer for generating one or more sets of M data symbols for mapping to first and second sets of M tones by performing a summation of a product of a set of M complex time domain data symbols and a set of M complex sinusoids corresponding to the first or second sets of M tones, respectively;
a mapping module for mapping the one or more sets of M data symbols to one or more symbol periods of a first dwell period and to one or more symbol periods of a second dwell period, the first dwell period comprising the first set of M tones allocated to the communications device for a first plurality of symbol periods, the second dwell period comprising the second set of M tones, wherein the second set of M tone are different than the first set and are allocated to the communications device for a second plurality of symbol periods;
a frequency to time domain transformer for processing, for each symbol period of the one or more symbol periods of the first and second dwell periods, a corresponding set of M mapped symbols to obtain the frequency division multiplexed signal for the each symbol period for the first and second dwell periods; and
a transmitter for transmitting the frequency division multiplexed signal in the wireless communication system.
22. The apparatus of claim 21 , wherein the second dwell period comprises a dwell period immediately following the first dwell period.
23. The apparatus of claim 21 , wherein the frequency to time domain transformer processes the corresponding set of M mapped symbols for the each symbol period according to a function that defines a continuous-time signal corresponding to the frequency division multiplexed signal for the each symbol period, and wherein the function comprises a summation of M sinusoids having coefficients corresponding to the set of M mapped symbols for the each symbol period.
24. The apparatus of claim 21 , further comprising:
a cyclic prefix inserter for prepending a cyclic prefix to the frequency division multiplexed signal.
25. The apparatus of claim 21 , wherein the first and second sets of M tones comprise M contiguous tones.
26. The apparatus of claim 21 , wherein the first and second sets of M tones comprise equally spaced tones.